Auxiliary apparatus for teletypers



March 26, 1963 B. c. w. HAGELlN ETAL 3,

AUXILIARY APPARATUS- FOR TELETYPERS Filed Dec. 31, 1958 Fig. 3

[NVENTORS Boms c.w. HAGELIN OSKAR STGRZIN E -fklkvbm ATT'O R NEYS 3,@83,Z63 Patented Mar. 26, 1963 AUXILIARY APPARATUS FOR TELETYPERS Boris Caesar Wilhelm Hagelin, Zug, and Oskar Sturzfinger, Bear, Switzerland, assignors to Anstalt Enropaische Handelsgesellschaft, Vaduz, Liechtenstein Filed Dec. 31, 1958, Ser. No. 784,144 Claims priority, application Switzerland Jan. 7, 1958 6 Claims. (Cl. 178-42).

The present invention relates to telecommunication equipment and more particularly to mixing apparatus to be used in conjunction with teletypewriting units, the purpose of such apparatus being the signal by signal coding and/ or decoding of messages to be supplied from the respective teletypewriting unit to a transmission line, and/ or vice versa.

In the teletyping technique of today, equipment is predominantly used which operates on the basis of the CCIT alphabet No. 2. In this alphabet, as well known, five impulses having each two possible forms, are used to characterize the letters, resulting in an assortment of 32 possible signal combinations.

rrangements are known today which permit the use of such teletypewriting systems in wireless communication as well, which fact puts the problem of secrecy to the fore. Therefore, Widely varying arrangements and supplementary equipments are already known for effecting automatic coding and decoding at the transmitting and receiving stations, and such supplementary equipments come more and more into use in wire-bound communication as well.

Fundamentally, these mixing equipments for signal-wise coding and/ or decoding may be divided into two classes. The first class comprises sets in which the signals are mixed with signals taken from a ready-made key sequence, e.g. in the form of a perforated tape, whereby usually a correlation is employed whereby the impulse No. 1 of each character always is mixed with the signal recorded in track number 1 of the perforated key tape (also called camouflage tapes), impulse of the character No. 2 is mixed with the signal recorded in track number 2, etc. The perforated tapes as a rule are advanced by one step per character and mixing takes place by using the four possible combinations between the respective signal impulse belonging to a character of the message and the corresponding key signal provided by the perforated tape to obtain a total of two possible results:

This arrangement ofiers the advantage that absolute security will be obtained if the key tapes have arbitrary sequences of perforations and are used once only.

The second class of mixing equipment comprises sets in which a computer-like key mechanism comprising preset adjustable members produces a key sequence which continuously develops itself further. The signals produced by these sets are mixed with the signals of the message in a manner similar to that in which the key tapes are effective, i.e. the key impulses produced by the key mechanism are combined with those of the text characters and the resulting impulses are transmitted.

The equipments of both classes have advantages and disadvantages. The advantage of the sets of the first class resides, as mentioned, in the mathematically absolute security, since in this case keys are used which, in the .so-called camouflage tapes, comprise a sequence of signals produced strictly by hazard and which never repeats itself. The drawback resides in that for a co-operation between two stations a key-tape supply organization must be available and moreover in the case of larger networks a considerable supply of key tapes of the most different kinds must be kept in store.

The sets of the second class are not absolutely safe from the mathematical point of view, though the arrangements known today produce key programs which practically cannot be detected with any calculating means whatsoever by unauthorized persons. Their advantage consists in that the key mechanism can be reset in simple manner for each message. The basic information required for this resetting will be formed as a rule of a few ciphers, so that bodily supply means are not required for the setting of the key and the stations own communication channel can be employed for the transmission of this key information.

It is now an object of the present invention to provide a mixing apparatus by means of which one or both kinds of coding can be effected as desired so that transmission can be effected under the control either of a mechanical key device or of a camouflage key tape, or under the control of both. This latter control method may be applied when the supply of new camouflage key tape is not possible while the use of purely mechanical control does not appear safe enough.

A further object of the invention is to provide an arrangement by which it is possible to feed a message into the apparatus alternately from the said teletypewriter or in the form of a pre-punched record in a perforated tape.

Still another object of the invention is to provide means whereby the apparatus while it is coding and transmitting a message, can immediately be switched to the reception of a message in uncoded form, by appropriate signals emanating from the station which is receiving the message. This makes it possible in case of disturbances that the transmitting and receiving stations agree without delay upon any appropriate measures for obviating the said disturbances.

Further objects and advantages of the invention will appear from its more detailed description with reference to the accompanying drawing which shows, by way of example:

In FIG. 1 a schematic wiring diagram of one embodiment of the invention;

In FIG. 2, in a partial schematic wiring diagram, a

modification of the embodiment shown in FIG. 1; and

In FIG. 3, in schematic form, the preferred general lay-out of the apparatus according to the invention.

In the circuits according to FIGS. 1 and 2, the information supplied as a conventional sequence of pulses from a teletypewriter is fed pulse by pulse from an input conductor A through normally closed switches Q and U1 (to be described later) to an input relay ER which controls a change-over switch er. According to the position of the latter, either a positive or a negative polarity signal is forwarded from a source H to a storage condenser C. Each signal thus stored in the condenser C is passed on through a conventional camshaft driven input distributor (not shown), an array of change-over switches l and v (FIG. 1), or v and r (FIG. 2) respectively, and a conventional camshaft driven output distributor (not shown) to one or the other end of an output relay winding SR the mid-point of which is grounded. Each of the change over switches l, v, and r has five individually controlled contact pairs, only one of which is shown in the drawings, which are sequentially connected into the circuit by the said input and output distributors, the camshafts of which are rotated in synchronism. The output relay winding SR controls a transmission contact sr which is in circuit with the outgoing line B through normally closed switches U2 and L0 the operation of which will be described later.

In the apparatus represented in FIG. 1, the change-over switch 1 is controlled by a perforated-tape scanner L, operating in synchronism with the aforesaid distributors,

According to the presence or absence of a hole in the respective track at the scanned point of the perforated tape running through the scanner, the respective contact pair of the change-over switch I supplies the received information signal either to one or to the other of the two branches of the doubled change-over switch v whereby, for any one condition of the respective contact pair of that switch, the signal is supplied either to the upper or to the lower end of the relay winding SR. The polarity of the latter depends on the combination of the polarity sign of the pulse received through switch er with the sign indicating the presence or absence of a hole at the scanned point of the tape running through the scanner L, according to the combination rule indicated above.

The double change-over switch v is controlled by a mechanical key permuting device V of the well-known kind constructed, for instance, somewhat like a mechanical computer and in which a plurality of key elements each controlling one pair of contacts of the switch v are displaced step by step. Thereby, for any one of the two conditions of the respective contact pairs of the tapecontrolled change-over switch I, the positive or negative signal pulse from switch er is again supplied either to the upper or to the lower end of the relay winding SR so that, when the switch I is not actuated, the polarity of the relay winding SR depends on the combination of the polarity sign of the signal pulse coming from switch er, with the sign or which designates the condition imparted to the double change-over switch v by the mechanical key permuting device V, the sign indicating the polarity of the relay SR being again derived from the two component signs of the combination according to the said rule.

Obviously, a double coding can be obtained by operating the scanner L and the permuting device V simultaneously. In this case the polarity of the relay SR is indicated by combining once more the sign indicating the output of the scanner-controlled change-over switch 1, with the sign indicating the position of the permuter-controlled switch v.

In the alternative mounting partly represented in FIG. 2, the perforated-tape scanner L of FIG. 1 and the changeover switch 1 controlled by it are replaced by the mechanical key-permuting device V and the change-over vswitch v controlled by it, which in this instance is not doubled since its function is similar to that of the single switch v of FIG. 1. On the other hand, the perforated-tape scanner L acts, through internal change-over switch means not shown in the drawing, on a relay R which in turn controls a double change-over switch r performing the same function as the double change-over switch v in FIG. 1. This arrangement makes it possible to introduce the message signals electrically through the key scanner L instead of through the input conductor A, and by means of a second perforated-tape scanner E while leaving the input relay ER inoperative. In this mode of operation, perofrated tapes are run both through the message tape scannerE and through the key tape scanner L. The message signals are derived from the perforations of the message key tape by internal change-over switch means which are controlled by the tape scanner E and which connect the scanner L either to the positive or to the negative pole of the source of potential I-I. Thus, depending on the information on the spot of the message tape which is being scanned in the scanner E, the respective contact pair of the changeover switch in the scanner L receives a positive or a negative potential. This is supplied to the upper or to the lower end ofthe relay winding R, according to the information on the spot of the key tape which is being scanned in the scanner L. Accordingly, the polarisation of the relay R, and the position of the double change-over switch r is defined by the combination of the signals read from the tapes in the two scanners E and L. The polarization of the transmitting relay SR and the position of the changeover switch sr controlled thereby is defined by the condition of the relay R and by the position of the switch v controlled by the mechanical key permuting device V.

With either of the arrangements represented in FIGS. 1 and 2, and owing to the combined effect of the keys obtained from key tape in the scanner L and from the key permuting device V, the same piece of key tape can be used several times. In theory, it would be possible to use it over and over again until all possibilities of varying the key by means of the mechanical key permuting device are exhausted tosuch a degree that the possibility would arise for an unauthorized person to reconstruct the series of keys punched into the key tape.

It would even be possible by means of this arrangement and of a receiving puncher to produce a multiplicity of new key tapes all derived from the same original key tape (which should have been produced according to the law of hazard) by combining the successive keys on the original tape with the successive keys produced by the permuting device. However, this procedure is useless where the stations at both ends are similarly equipped, since it is to no purpose to prepare a multiplicity of key tapes when the keys recorded thereon could be produced mechanically in a continuous manner at both ends, by using the original key tape and setting similarly the key permuting device at both ends.

The apparatus diagrammatically represented in FIG. 3 is in the form of a self-contained set comprising a num ber of pre-assembled block units of which those which are not required could be omitted, disconnected, or switched out of circuit. Thus, it is possible to produce or use the set as an apparatus for the automatic coding of messages either by means of a ready-made sequence of keys supplied on a key tape, or by means of keys derived by automatic permutation of the signs of a key to which the permuting device has been set initially, or for double coding by both means.

In FIG. 3, RB designates a relay block or unit com prising the required relays as shown in FIG. 1 or FIG. 2, M is an electric motor for driving the various units in synchronism, G is a set of gear wheels provided for that purpose, T is a unit similar to a conventional regenerating repeater and comprising the'timing camshafts, E is the message tape scanner used in the mounting shown in FIG. 2, L is the key tape scanner and V is the mechanical key permuting unit used in both mountings according to FIGS. 1 and 2; T, E and L are actuated by the same shaft while the permuting device V is driven by a separate shaft.

The invention also comprises a number of provisions to suit particular operating conditions and which now will be described with reference to FIG. 1.

In the practical operation of teletypewriters it often occurs that the receiving set drops out of synchronism with the transmitting set. In clear operation, this will not have any greater consequences since at the most one letter or equivalent group of signals Will be mutilated. However, where a key permuting device is actuated step by step, such dropping out of synchronism causes all subsequent letters or signal groups to be decoded wrongly so as to become unintelligible, since the key provided by the permuting device of the receiving set no longer is the same as that simultaneously provided by the corresponding device of the transmitting set. Now, in the conventional teletypewriting system, each letter or information group of signals is preceded by a break pulse and followed by a stop pulse If in that system, the receiving set drops out of synchronism with the transmitting set, it is the usual practice to let the receiving set transmit a continuous break pulse to the line. Whenever the system contains an automatic direction change-over means, the transmitting station then will run off since it will be re-started by the continuous break pulse immediately after each stopping. This running ofi of the trans mitting set will be noticed by the operator and will induce him to switch over to clear operation, in order to agree with his partner upon any measures to be taken.

However,- When in the transmitting station a perforatedtape message transmitter is used as described with reference to FIG. 2, this method of calling the transmitting operators attentions from .the receiving station is inefiective since the units of the transmitting station anyhow run at the highest possible speed, so that any running ofi hardly would be noticeable; moreover, even though the transmitting station Were switched to reception by the break pulse emanating from the receiving station the operator of which desires to make himself noticed, the transmitting station would immediately be switched back to transmission so long as its own message tape scanner operates. Thus, the receiving station must remain inactive in this case until the message tape has passed through the scanner entirely, and it can make itself noticeable only then, which fact may lead to great loss of time.

According to a feature of the present invention, the apparatus may comprise an automatic switching means K which is immediately responsive to any break pulse coming in from the transmission line B regardless of whether the apparatus is transmitting clear or coded text. If such a break pulse comes in while the apparatus is not operating, it will cause the switching means K to condition the apparatus for reception. For this purpose, a pair of relay-controlled switches U1 and U2 are provided in the connection between the input line A and the input relay ER, and in the connection between the output switch sr and the transmission line B, respectively. These switches U1 and U2 are so connected that when the switching means K causes their controlling relays (not shown) to be energized in response to the coming-in of a break pulse through line 'B, switch U2 will break the connection between output switch sr and line B and connect the latter to the input relay ER, and switch U1 will disconnect that relay ER from the line A coming from .the teletypewriter but connect the output from the switch sr to the said line A leading to the teletypewriter. Thus the apparatus is ready for passing messages from the line B through input relay ER/er, any interposed change-over switches, and output relay SR/sr, to the teletypewriter.

Besides, a switch D is provided in the connection between the condenser C and the output relay SR. This switch D is under the combined control of the switching means K and of an additional normally open pair of contacts controlled by the distributor mechanism indicated at T in FIG. 3, this pair of contacts being closed each time the distributor leaves its rest position and reopened only when it reaches that position again. In its normal position shown in FIG. 1, the said switch D connects the condenser C to the first change-over switch I. In its opposite position, however, which it assumes when both the switching relay K is energized and the pair of contacts controlled by the distributor mechanism is closed, the switch D connects the condenser C to a bypass line which shunts the keying change-over switches l and v and leads directly to the lower end of the output relay SR. Thus, whenever the apparatus receives a break pulse through line B while the distributor unit T is working, not only will the switches U1 and U2. be moved by the switching means K from their transmitting position as shown in FIG. 1 to their receiving position in which the signals received through line B are fed to the input relay ER and from the output relay switch sr to the teletypewriter connection A, but at the same time the output relay SR will be connected to the condenser C by a direct line shunting the keying change-over switches l and v. Accordingly, the message initiated by the break pulse from the receiving station while the considered station is transmitting is not passed through these change-over switches but is available in clear text.

In this manner, the receiving station may be switched in at any time and may even, when transmisison is made from a message tape, write back immediately without requiring the operator of the initially transmitting station to effect any manipulation since by the break pulse signal his station has been switched from transmission to reception. This is quite important for immediate agreement on the measures to be taken in case of faulty transmission, and saves much time since the operator of the initially transmitting station can readily be informed about the reasons why a break pulse signal was given. If the mixing apparatus of the initially transmitting station is equipped with a mess-age tape transmitter, this will immediately be stopped by the automatic break-pulse responsive switching device K and the whole apparatus is again switched to reception.

A further switch Q which controls the connection between the input A from the teletypewriter and the apparatus is controlled jointly with the clear/ coding switch D to interrupt the said connection as the switch D is moved to the clear position. Thereby, even though any message tape scanner in the teletypewriter would continue to operate, the message scanned there would no longer be fed into the apparatus.

If the apparatus itself contains a message tape scanner such as that indicated at E in FIG. 2, a switch similar to, and operated in the same manner as, the switch Q just described will be provided to disconnect or stop that message tape scanner.

A further relay S controlling a signal lamp and buzzer alarm device R is connected to the switching relay K in such a manner as to be energized each time the latter is actuated by an incoming break pulse as described. The operators attention will then be called by the alarm device R to the incoming message. In order that this condition may be distinguished from others in which the alarm device R is operated, a modulating relay Z is connected to the switching means K to modulate the signal forwarded to the relay S.

In case of a very much disturbed transmission, it is customary to prepunch the coded message text on a tape, so that it can be transmitted several times in succession. At the receiving station a tape recorder is connected to the line; the operator then compares the several perforated tapes thus obtained with each other, whereupon they are decoded in a local circuit.

This method requires much time, but offers the advantage that synchronization problems are practically eliminated in so liar as the key tape scanner and keying units are concerned. In the present apparatus, a mum ually operable switch L0 is provided for this purpose. This switch L0 is arranged to connect the output of the apparatus in a first and normal position to the transmission line B, and in a second position to a local line through which the coded message delivered by the output switch sr is fed back to the teletypewriter through A, where it may be delivered to an appropriate tape recorder provided for such purposes.

Jointly with the moving of the switch Lt into its second position a relay UE is rendered sensitive to any signals coming in through the transmission line B thus disconnected. On receipt of any signal through E while UE is sensitive, relay S is energized and causes the alarm device R to call the operator who then may take appropriate steps for receiving the message thus announced.

For so-called Telex operation, the teletypewriters are equipped with automatic call sign transmitters which in response to the receipt of CCITT combination No. 4 (the signal corresponding to the letter D in the numerals series) automatically transmit the stations own call sign to acknowledge receipt of the call.

Now, if in the present apparatus a coded text is being received and directly forwarded to a tape recorder to be recorded for later decoding, it might occur that the coded text happens to contain the said combination No. 4, in which case [the receiving stations automatic call sign transmitter would be started and interfere with the transmission unless the occurrence of combination No. 4 were not already prevented in known manner in the course of coding. However, with the present mixing apparatus this 7 can be avoided by means of the switching means K since in this case the apparatus is switched intentionally to clear transmission and merely operates as a regenerative repeater. After having actuated the receiving stations automatic call sign transmitter a first time in the usual manner for establishing the communication, the operator 7 f the calling station iactuates the said automatic call sign transmitter of the receiving station a second time and immediately starts transmitting. Thereby, the break pulse responsive switching means K at the receiving station is actuated since that stations call sign transmitter is run ning; thereby, the rest contact Q of the local line is opened and transmission is blocked.

To ensure resumption of the correct operation of the receiving station as soon as possible after transmission of the message is completed, a timer switch NG is provided in the connection to the relay which operates switch Q. Thereby, switch Q will automatically be closed to seconds after the last signal has been transmitted. Obviously, it is possible to provide a signalling device to signify to the operator at the transmitting station when switchQ is closed again.

We claim:

1. Apparatus for the automatic coding or decoding of mess-ages constituted by successive electric signals in teletypewriting systems comprising an input conductor for connection with a teletypewriting unit, and output conductor for connection with a transmission line, a repeater device having an input and an output and including signal modifying means for transmitting signals in selectively modified form from said input to said output, by-pass conductor means for transmitting such signals in unmodified form from said input to said output, by-passing switch means for selectively connecting in a first position said signal modifying means and and in a second position said by-pass conductor means between said input and said output, and means for sensing the operative or inoperative condition of said repeater device, said apparatus further comprising reversing switch means connected between said input conductor and said repeater input and between said repeater output and said output conductor for selectively connecting in a first position said input conductor to said repeater input and said repeater output to said output conductor, and in a second position said output conductor to said repeater input and said repeater output to said input conductor while disconnecting said input conductor from said repeater input and said repeater output from said output conductor, means connected at said repeater output and responsive to at least one predetermined signal coming in through said output conductor for automatically throwing said reversing switch means from its said first position into its said second position on reception of said predetermined signal, and conditionable by said repeater operation sensing means for automatically throwing said lay-passing switch means from its said first position into its said second position on reception of said predetermined signal while said repeater device is in its said operative condition.

2. Apparatus as claimed in claim '1, which further comprises a normally closed breaker switch in the connection between said input conductor and said repeater input on the input conductor side of said reversing switch means, the said signal-responsive means being operatively connected to said breaker switch for automatically opening it on reception of said predetermined signal while said repeater device is in its operative condition.

3. Apparatus as claimed in claim 2, which further comprises a timer switch operatively connected to said signal-responsive means for causing them to close said breaker switch a predetermined time after the cessation of signals coming in through said output conductor.

4. Apparatus as claimed in claim 1, which further eom-. prises an alarm device and means operable by said signalresponsive means for actuating said alarm device on reception of said predetermined signal by said signal-responsive means while said repeater device is in its said operative condition.

5. Apparatus as claimed in claim 1, which further comprises a local operation switch for selectively connecting said repeater output in a first position to said output conductor and in a second position to said input conductor.

6. Apparatus as claimed in claim 5, which further comprises an alarm device and a relay conditionable by said local operation switch as the latter assumes its said second position to become responsive to said at least one predetermined signal for on reception thereof actuating said alarm device.

References Cited in the file of this patent UNITED STATES PATENTS 1,310,719 Vernam July 22, 1919 2,028,818 Anspach Jan. 28, 1936 2,504,621 Bacon Apr. 18, 1950 2,547,515 Zenner Apr. 3, 1951 

1. APPARATUS FOR THE AUTOMATIC CODING OR DECODING OF MESSAGES CONSTITUTED BY SUCCESSIVE ELECTRIC SIGNALS IN TELETYPEWRITING SYSTEMS COMPRISING AN INPUT CONDUCTOR FOR CONNECTION WITH A TELETYPEWRITING UNIT, AND OUTPUT CONDUCTOR FOR CONNECTION WITH A TRANSMISSION LINE, A REPEATER DEVICE HAVING AN INPUT AND AN OUTPUT AND INCLUDING SIGNAL MODIFYING MEANS FOR TRANSMITTING SIGNALS IN SELECTIVELY MODIFIED FORM FROM SAID INPUT TO SAID OUTPUT, BY-PASS CONDUCTOR MEANS FOR TRANSMITTING SUCH SIGNALS IN UNMODIFIED FORM FROM SAID INPUT TO SAID OUTPUT, BY-PASSING SWITCH MEANS FOR SELECTIVELY CONNECTING IN A FIRST POSITION SAID SIGNAL MODIFYING MEANS AND AND IN A SECOND POSITION SAID BY-PASS CONDUCTOR MEANS BETWEEN SAID INPUT AND SAID OUTPUT, AND MEANS FOR SENSING THE OPERATIVE OR INOPERATIVE CONDITION OF SAID REPEATER DEVICE, SAID APPARATUS FURTHER COMPRISING REVERSING SWITCH MEANS CONNECTED BETWEEN SAID INPUT CONDUCTOR AND SAID REPEATER INPUT AND BETWEEN SAID REPEATER OUTPUT AND SAID OUTPUT CONDUCTOR FOR SELECTIVELY CONNECTING IN A FIRST POSITION SAID INPUT CONDUCTOR TO SAID REPEATER INPUT AND SAID REPEATER OUTPUT TO SAID OUTPUT CONDUCTOR, AND IN A SECOND POSITION SAID OUTPUT CONDUCTOR TO SAID REPEATER INPUT AND SAID REPEATER OUTPUT TO SAID INPUT CONDUCTOR WHILE DISCONNECTING SAID INPUT CONDUCTOR FROM SAID REPEATER INPUT AND SAID REPEATER OUTPUT FROM SAID OUTPUT CONDUCTOR, MEANS CONNECTED AT SAID REPEATER OUTPUT AND RESPONSIVE TO AT LEAST ONE PREDETERMINED SIGNAL COMING IN THROUGH SAID OUTPUT CONDUCTOR FOR AUTOMATICALLY THROWING SAID REVERSING SWITCH MEANS FROM ITS SAID FIRST POSITION INTO ITS SAID SECOND POSITION ON RECEPTION OF SAID PREDETERMINED SIGNAL, AND CONDITIONABLE BY SAID REPEATER OPERATION SENSING MEANS FOR AUTOMATICALLY THROWING SAID BY-PASSING SWITCH MEANS FROM ITS SAID FIRST POSITION INTO ITS SAID SECOND POSITION ON RECEPTION OF SAID PREDETERMINED SIGNAL WHILE SAID REPEATER DEVICE IS IN ITS SAID OPERATIVE CONDITION. 